Recently, in semiconductor devices such as DRAM and FeRAM, a high dielectric-constant film such as Ta2O5 is used as a capacitance insulating film in order to ensure a necessary accumulated capacitance in a small occupied area and to improve a degree of memory cell integration.
When such a high dielectric-constant film is used for the capacitance insulating film, it is important to select a material which does not form an insulating film by oxidization as a material of electrodes sandwiching the capacitance insulating film. Oxygen is liberated from such a high dielectric-constant film in a thermal treatment process of a semiconductor device, and the electrodes made of polysilicon or the like are oxidized to form an oxide film with a low dielectric-constant, leading to reduction in capacitance.
As an electrode material which does not cause such a capacitance reduction, much attention is paid to ruthenium recently. Ruthenium has electric conductivity, even if it is oxidized, and it is inexpensive, which makes it favorable as an electrode material.
However, when an electrode is formed using ruthenium, ruthenium-based metal (ruthenium, ruthenium oxide or the like) may adhere to the end face or the rear face of the silicon substrate, and its peeled materials may adhere to the device forming area and may cause cross-contamination between the devices and between the wafers via the transfer system. Since ruthenium-based metal is known as so-called a lifetime killer for a semiconductor device, and has a high diffusion rate, if only a little ruthenium-based metal remains on the silicon substrate surface, the device properties may be reduced and reliability of the devices may be impaired.
Especially, in recent years, forming a electrode film in a narrow hole is demanded to reduce the occupied area of a capacitor, and from the necessity of forming a uniform ruthenium-based metal film with a small film thickness, the necessity of forming the film with use of a CVD method having good coverage ability increases. If the film is formed according to such a CVD method, ruthenium-based metal adheres to the end face and the rear face of the silicon substrate more heavily, and the above-described problem becomes more serious.
In order to solve the above problem, it is important to remove unneeded ruthenium-based metal by treatment using a chemical solution after forming a ruthenium-based metal film.
There are few chemical solutions which can sufficiently dissolve and remove the ruthenium-based metal, but Japanese Patent Laid-open No. 2001-234373 and Japanese Patent Laid-open No. 2001-237389 disclose a remover solution comprising salt including quadrivalent cerium ion or periodic acid and a specified acid as chemical solution suitable for cleaning wafer. Especially in Japanese Patent Laid-open No. 2001-234373, a detailed study results about the remover solution comprising (a) cerium (IV) nitrate salt, and at least one acid selected from the group consisting of (b) nitric acid, perchloric acid and acetic acid are described.
Further, as a method of using the above-described chemical solution, Japanese Patent Laid-open No. 2001-234373 discloses a method of removing ruthenium-based metal adhering to the area except the device forming area by holding a semiconductor substrate substantially horizontally to rotate it after forming a ruthenium-based metal film on the semiconductor substrate, and by spraying the remover solution onto a predetermined area while spraying a nitrogen gas onto the device forming surface of the semiconductor substrate. It is described that in this method, the remover solution is in contact with only the end face and the rear face of the substrate by spraying the nitrogen gas onto the device forming surface of the semiconductor substrate.
Further, Japanese Patent Laid-open No. 2001-237389 discloses a method for manufacturing a semiconductor device comprising a step of holding the semiconductor substrate substantially horizontally to rotate it after forming the ruthenium-based metal film, spraying the remover solution onto predetermined parts while spraying a gas or a liquid onto the surface having an device forming area of the semiconductor substrate and removing the ruthenium-based metal adhering to areas other than device forming area.
Incidentally, there are a single wafer type and a batch type as a wafer cleaning or wet etching apparatus. A single wafer type of apparatus is for transferring wafers into the treatment tank to treat it one by one, in which a liquid is sprayed to the surface of the wafer while the wafer is rotated, that is a spinning method, so that washing or etching is performed. The aforementioned method of removing ruthenium-based metal is performed using the single wafer type of apparatus with the spinning method. On the other hand, the batch type of apparatus is for treating a plurality of wafers in the treatment tank at one time, in which a plurality of wafers are arranged in line to immerse them at one time, that is a dip method, so that washing or etching is performed.
As the single wafer type of apparatus, Japanese Patent Laid-open No. 10-223593 discloses a single wafer type wafer cleaning apparatus which cleans a wafer in the state of floating and rotating in a predetermined direction, and comprising a cleaning tank having a first blast port for blasting a cleaning solution from the side of a top surface of the wafer, and a stage having a second blast port for blasting the cleaning solution from the side of a undersurface of the wafer, and performing cleaning by allowing the cleaning solution blasted out from the first and second blast ports to spread uniformly over the entire top surface and the entire undersurface of the wafer by a centrifugal force by the rotation of the wafer. It is also described that a blast port for floating and a blast port for rotation are set up around the second blast port of the stage, and mediums such as pure water and air are blasted from these blast ports in order to rotate the wafer in the predetermined direction while floating it. Further, waste liquid of the cleaning solution accumulated in the cleaning tank is recovered by the waste liquid treatment apparatus via a waste liquid discharge passage set up at the bottom of the cleaning tank, and is subjected to filtering treatment to be reused.
On the other hand, as a batch type (dip type) of apparatus, Japanese Patent Laid-open No. 3-108333 discloses a wet etching apparatus including a treatment tank in which an object to be treated is in contact with an etching solution composed of hydrofluoric acid, and a circulation passage for circulating the etching solution into the treatment tank, and having a reaction product removing device, which is constructed to heat the etching solution to gasify reaction products and discharge the gas outside the solution, in the circulation passage.